Comparing Wave Force and Wave-Induced Overturning Moment of Three Offshore Support Structures

In this study, in order to investigate wave force and wave-induced overturning moment according to the support structure types and sea levels, wave force tests were carried out for the three offshore support structures of Monopile, GBS, and Hybrid under three sea levels of HSWL, MSL, and LSWL. As the results of this study, it was found that, as the wave height increased at the shallow water (LSWL), wave force increased significantly because of the wave nonlinearity, named wave shoaling. Also, as the structural member size became larger, wave nonlinearity effects on wave force at the shallow water (LSWL) were reduced because of the wave diffraction effect of the large-sized member. Accordingly, variations of wave force and wave-induced overturning moment according to the wave heights and sea levels were larger in the slender member and smaller in the large-sized member. Therefore, it was concluded that wave force and wave-induced overturning moment of the large-sized support structure were little sensitive to the wave height and sea level than the slender support structure. Maximum overturning moments occurred at the HSWL in the Monopile, at the MSL in the GBS, and at the LSWL in the Hybrid, respectively.